Escitalopram is a well-known antidepressant drug that has the following structure:

It is a selective, centrally active serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor, accordingly having antidepressant activities.
Escitalopram and the pharmaceutical activity thereof are disclosed in U.S. Pat. No. 4,943,590. Two methods for preparation of escitalopram are disclosed. In one of them 4-[4-(dimethylamino)-1-(4′-fluorophenyl)-1-hydroxybutyl]-3-(hydroxymethyl)-benzonitrile is fractionally crystallized as a salt with (+)-O,O′-di-p-toluoyl-(S,S)-tartaric acid in 2-propanol. The crystalline product produced in this way consists of small crystals that drain very slowly and tend to retain the mother liquors. Insufficient removal of the mother liquors gives a product with a low enantiomeric purity and therefore additional purifications are required. Purifications are time and solvent consuming. These problems are more evident on an industrial scale.